The present invention relates generally to ultrasonic bonding in semiconductor packaging applications. More particularly, an improved method and apparatus for adjusting the bonding parameters based upon multidimensional feedback is disclosed.
In semiconductor packaging, lead frames are commonly used to couple a die to external components. Most commonly, the bonding pads on the dies are electrically coupled to associates leads on the lead frame using bonding wires. One end of each bonding wire is typically ultrasonically bonded to a die pads on the die and the opposite end is typically bonded to an associated lead. In some applications (particularly small high lead count packages) it may be desirable or necessary to use an interposer in conjunction with the lead frame. The interposer is similar to a mini printed circuit board. A conventional method for connecting a bonding pad to an associated lead via an interposer is commonly referred to as lead frame-interposer integration. The bonding wires are typically ultrasonically bonded to their associated contacts. In contrast, during lead frame-interposer integration, the leads of a lead frame are bonded directly onto the traces on an interposer. For example, an overlapping lead and its associated trace are ultrasonically bonded at a single point.
Referring initially to FIG. 1, a conventional ultrasonic bonder arrangement that is suitable for lead frame-interposer integration will be schematically described. The bonder 100 has a bonding tool 112, a transducer 110 having a support section 118, a base 122, a plurality of fasteners 114, a plurality of mount holes 116, and a plurality of base holes 120. The bonding tool 112 is attached to one end of the transducer 110, while the base 122 is attached to the other end of the transducer 110. The transducer 110 is attached to the base 122 by inserting each fastener 114 into a mount hole 116 within the support section 118 and then into a base hole 120 within the base 122.
Referring now to FIG. 2, the lead frame-interposer integration process will now be described. During lead frame-inter poser integration, the bonding tool 112 is used to ultrasonically bond a lead 124 directly onto an associated trace 128 on the interposer 126. For a bond to occur, the bonding surfaces (lead 124 and trace 128) need to be in direct contact during the ultrasonic bonding. Additionally, the bonding surfaces must remain motionless with respect to each other. The ultrasonic energy 132 is then transmitted through the lead 128 to the underlying trace 128 on the interposer 126. In effect, the ultrasonic mechanical vibration 132 of the bonding tool 112 is translated into molecular vibration 130 in the lead 124 and the trace 128. This molecular movement 130 results in an intermetallic bond between the lead and trace.
During a wire bonding process (not shown), in contrast to a lead frame-interposer integration process, the bonding tool takes the form of a capillary that is firmly secured by a capillary holder by a lock screw and is arranged to feed a bonding wire as necessary. Typically, the distal end of the bonding wire is initially ultrasonically bonded to a die pad on an integrated circuit. This is typically accomplished by a process known as ball bonding. When the first end of the bonding wire is firmly adhered to the die pad, the transducer and capillary arrangement is moved to a position over a lead of the lead frame. As the transducer is moved, the bonding wire is fed through the capillary. The bonding wire is then ultrasonically bonded to the associated lead and the continuous feed wire is cut off so that a short and discrete bonding wire is formed between the die pad and the lead. The ultrasonic bonding to the lead is typically done by a process referred to as stitch bonding.
Unfortunately, these conventional bonding systems and processes have certain drawbacks. First, the high power required for bonding certain thick materials can also destroy intermetallic formation if the power is applied to the bonding material for too long a time period. This problem is especially prevalent in lead frame-interposer integration since the ultrasonic energy must be great enough to be transferred through the relatively thick lead to the trace on the interposer. Second, various ultrasonic energy levels are required for different bonding configurations. For example, when the lead's longitudinal axis is parallel to the direction of the bonding tool's movement, more energy could be applied than when the lead's axis is perpendicular. This factor complicates the determination of the proper bonding duration before destruction occurs. Thus, a way to improve the controlling mechanism of the bonding duration of these bonding systems is highly desirable.